Permanent magnet materials are believed to be composed of small regions or “domains” each of which exhibit a net magnetic moment. An unmagnetized magnet will possess domains that are randomly oriented with respect to each other, providing a net magnetic moment of zero. Thus a magnet when demagnetized is only demagnetized from the observer’s point of view. Magnetizing fields serve to align randomly oriented domains to give a net, externally observable field.
The Orientation Direction
Some applications require magnets oriented in a particular direction with a high degree of accuracy. This direction may or may not coincide with a geometrical plane of the magnet. For anisotropic materials the orientation direction can normally be held within 3° of the nominal with no special precautions. However, more precise requirements may need special measurement and testing. This is achieved by the use of Helmholtz coils, which measure the total flux in various axes, and thence calculating the resultant magnetic moment vector. Materials must be cut and machined taking into account the actual angle of orientation to achieve the required accuracy. Isotropic materials may be magnetized in any direction, and therefore pose no problem in this regard.